1. Field of the Invention
This invention relates broadly to dental devices. More particularly, this invention relates to a device for accurately matching colored dental standards to natural teeth.
2. State of the Art
Prior to the process of implanting a dental prosthesis (or prosthetic tooth) in the mouth of a dental patient, a dentist must make a decision as to the color to be used for the dental prosthesis such that dental prosthesis appears natural when implanted adjacent natural teeth. To assist the dentist in making a decision, dental standards are available to permit the dentist to compare the standards against the natural teeth. The standards are typically preformed dental prostheses of a variety of colors, saturations, or hues, attached to the end of a thin metal rod. Once the dentist decides which standard is closest in color to the natural teeth, the appropriate color for the prosthetic is thereby chosen.
However, choosing the correct color standard relative to natural teeth is often difficult. One difficulty lies in that natural teeth are translucent and, as a result, the type of light in which they are viewed can affect their apparent color. For example, tooth color appears to change when viewed in fluorescent light and then polychromatic light (or white light) such as daylight. However, dental offices are typically lit with fluorescent lighting. Some dentists have used standard incandescent bulbs to provide a wider spectrum of light when comparing standards to the natural teeth. However, standard incandescent bulbs do not provide the broad polychromatic spectrum of light necessary to properly evaluate the standards relative to the natural teeth. Tooth color also appears to change when viewed in direct light and shadow. Furthermore, the background against which natural teeth and standards are viewed can alter the color appearance of the standards relative to the natural teeth. Moreover, natural teeth are multicolored, and the process of selecting the color for the prothesis requires a careful assessment of the topography and predominant color of the natural teeth, especially the teeth which will be adjacent the implanted prosthesis.
Therefore, a number of devices have been proposed to assist a dentist in choosing the color for a dental prosthesis tooth. U.S. Pat. No. 3,436,157 to Adler discloses a prismatic comparator device using a polychromatic light source which enables natural teeth to be simultaneously viewed with standards for comparison. The device however is cumbersome comprising four relatively long tubes, of which the ends of two must be inserted in the patient's mouth to abut the patient's natural teeth. In addition, the light source is a projection bulb, requiring a large amount of power (i.e., an AC power source) for illumination and generating a large amount of heat.
Other devices attempt to remove dentist subjectivity and determine the appropriate color for a prosthetic tooth based on an objective determination of the appropriate tooth color. For example, U.S. Pat. No. 5,383,020 to Vieillefosse discloses a device which uses a spectrometer to measure the reflectance of a natural tooth surface, amplifies the reflectance signal, converts the amplified reflectance signal to a digital signal, and processes the digital signal to provide an output purportedly helpful in determining prosthetic tooth color. U.S. Pat. No. 5,428,450 to Vieillefosse et al. discloses another electronic device. The device illuminates a portion of the natural tooth with a uniform and isotropic diffuse "light flux" and receives the light backscattered from the tooth. The backscattered light is then spectrally analyzed to purportedly determine the appropriate color for a prosthetic tooth. U.S. Pat. Nos. 3,986,777 to Roll, 4,654,794 to O'Brien, and U.S. Pat. No. 4,836,674 to Lequime et al. disclose other electronic spectrometric devices. However, these device are complicated and costly to manufacture. In addition, these devices do not account for the fact that teeth are multicolored. Aiming the device at one portion of natural tooth may provide results which differ when the device is aimed at another portion of the tooth, such that a subdominant color value, rather than the predominant color value, is used for selecting the color for the dental prosthesis. Moreover, the human eye, which will eventually judge the finished product, is removed from the comparison process.